Data from: Mechanisms and fitness consequences of laying decisions in a migratory raptor

Seasonal decline in breeding performance is a commonly observed pattern in
birds, but disentangling the contributions of environmental conditions
(“timing” hypothesis) and individual quality (“quality” hypothesis) to
such a pattern is challenging. Moreover, despite the strong selection for
early breeding, the individual optimization model predicts that each
individual has an optimal breeding window. We investigated the causes and
consequences of laying decisions in the lesser kestrel (Falco naumanni) by
combining a long-term dataset on reproductive traits with information on
food availability. A marked seasonal decline was found in breeding
success, mostly mediated by a decline in clutch size. The “timing”
hypothesis, supported by the decline in consumption of mole crickets, key
prey for prelaying females, seems to explain the seasonal trend in clutch
size, as this pattern was recorded in both higher (adults) and lower
(yearlings) quality individuals. Contrarily, the higher proportion of
yearlings breeding late in the season, rather than a decay in food
availability during chick rearing, seems to drive the decline in fledging
success, giving support to the “quality” hypothesis. Advanced breeding and
increased clutch size, as proxies of reproductive effort, were not offset
by lower survival. Low repeatability in both these traits suggests that
individual quality is a dynamic attribute and reproduction costs are
minimized by individual optimization. Understanding the mechanisms driving
individual breeding decisions is critical to anticipate species’ ability
to cope with environmental changes. Here, we show that lesser kestrels
failing the prelaying food window opportunity compromise reproductive
performance, mostly regardless of their individual quality.